Add warning for unrecognized references

this PR fix the warning on any on recognize reference due to wrong formatting or wrong place. closes #38.
@pksunkara so do you think this would work:

           ss << "Found a possible [" << symbol << "] reference but parsing it as an asset; ";
           ss << "If it needs to be parsed as a reference, it have to be directly after `Responses` or `Requests` and it's expected to be indented by 4 spaces or 1 tab";